To determine the type of metabolites, the time of generation and the metabolic pathways of transformation of the inositol phosphates, (InsP) produced upon T lymphocyte activation. The activation of an inositol phospholipid (InsPL)-specific phospholipase C (PLC), with consequent hydrolysis of membrane phospholipids is an early event associated with T cell receptor (TCR/CD3) / antigen (Ag) interaction. This metabolic pathway produces a series of InsP, which may be involved in cell activation by mobilizing Ca2+ from either endogenous or extracellular compartments. A consistent amount of evidence indicates that Ins (1,4,5) P3 metabolism may play a crucial role in the regulation of Ca2+ metabolism. Ins)1,4,5) P3 is directly involved in Ca2+ mobilization from intracellular stores. Studies performed in platelets and brain tissues demonstrated that Ins (1,4,5) p3 may be hydrolyzed to Ins (1,4) P2 by a specific 5-phosphomonoesterase (5PME) or phosphorylated by a 3- kinase (3K) to Ins (1,3.4,5) P4. Ins (1,4) P2 appears to be deprived of biological activity, while Ins (1,3,4,5) P4 may act as a Ca2+ mobilizer by opening certain sensitive membrane channels. The higher phosphorylated InsP5 and InsP6 may also have biological significance. The present project proposed to investigate the regulation of Ins (1,4,5) p3 metabolism in human and murine T-lymphocytes in response to perturbation of the TCR/CD3. Preliminary results indicate that intracellular Ca2+ modulates PLC activity. Furthermore, Ca2+ also control the rate on conversion of Ins (1,4,5) P3 to Ins (1,3,4,5) P4 and may also affect the catabolic rate of InsP3 to the less phosphorylated species. The catabolism of Ins (1,3,4,5) P4 was apparently unaffected by Ca2+ , except when increased up to the (unphysiological) high micromolar range. Conditions whereby different activation pathways may be simultaneously triggered will also be given special attention. This refers in particular to T cell activation by Ag in the presence of Ag- presenting, "accessory" cells with the consequent interaction with "accessory" and/or adhesion molecules. Activation of other signal transduction mechanisms, such as cAMP or cGMP by proper ligands (i.e.: prostaglandins) will also be considered regarding their effect on the generation of the InsP isomers.